Continuous process of producing shaped metallurgical coke

ABSTRACT

IMPROVED PROCESS OF PRODUCNG SHAPED COE ARTICLES MADE BY PELLETIZING COAL WITH OR WITHOUT ADMIXTURE THEREWITH OF COKE AND/OR MINERALS SUCH AS ORE, WHICH PROCESS CARBONIZES THE SHAPED ARTICLE IN A FIRST STAGE FOR ABOUT 2 TO 5 MINUTES WITH A CONCURRENT SOLID, PARTICULATE HEAT CARRIER AT ABOUT 500 TO 600* C.; A SECOND STAGE FOR ABOUT 30 TO 90 MINUTES WITH A COUNTER-CURRENT OR TRANSVERSE CURRENT   SOLID, PARTICULATE HEAT CARRIER HAVING AN INITIAL TEMPERATURE OF ABOUT 400 TO 500* C. INCREASING TO A FINAL TEMPERATURE OF 500 TO 600* C.; AND THEN IN A THIRD STAGE WITH A COUNTERCURRENT OR TRANSVERSE CURRENT SOLID, PARTICULATE HEAT CARRIER HAVING AN INITIAL TEMPERATURE OF ABOUT 550 TO 650* C. INCREASING TO A FINAL TEMPERATURE OF 850 TO 1000* C.

Oct. 24, 1972 J. wlLLlBALD ErAL 3,700,564

CONTINUOUS PROCESS OF PRODUCING SHAPED METALLURGICAL COKE Filed Sept. 4,1969 www .r w C1 N Hrw a T qmwT m n n In Tow United States Patent O U.S.Cl. 201-6 5 Claims ABSTRACT OF THE DISCLOSURE Improved process ofproducing shaped coke articles made by pelletizing coal with or withoutadmixture therewith of coke and/or minerals such as ore, which processcarbonizes the shaped article in a iirst stage for about 2 to 5 minuteswith a concurrent solid, particulate heat carrier at about 500 to 600C.; a second stage for about 30 to 90 minutes with a counter-current ortransverse current solid, particulate heat carrier having an initialtemperature of about 400 to 500 C. increasing to a final temperature of500 to 600 1C.; and then in a third stage with a countercurrent ortransverse current solid, particulate heat carrier having an initialtemperature of about 550 to 650 C. increasing to a final temperature of850 to 1000 C.

This invention relates to the production of shaped metallurgical cokefrom coals having dilferent caking and expansion properties. The presentinvention refers to a process of continuously producing shapedmetallurgical coke by a carbonization of shaped articles which have beenmade by a pelletizing or briquetting operation from ground coal, withoptional admixtures of ne coke or minerals, and a binder, whichcarbonization is effected with the aid of a dine-grained, solid heatcarrier.

Shaped metallurgical coke of uniform particle size is increasinglypreferred by the iron and steel industry because the use of preshaped orpelleted ore and of uniform pieces of sinter for charging blast furnacesis increasing and the efficiency of the blast furnaces is increased bythe use of coke having a uniform particle size. For use in metallurgicalfurnaces, the shaped charge stock, whether ore or coke, must have a highwear resistance, resistance to deformation, and crushing strength.

To enable an operation of a blast furnace at its highest etliciency, itis desirable to use a shaped coke which has the same weight per piece asthe preshaped ore. lExperience has shown that the most desirable weightof the shaped coke is about 30-50 grams per piece. The shaped particlesor pieces should have high crushing and abrasive strengths and shouldhave no protruding edges. They should have such a shape as to promotethe formation of relatively large voids in the blast furnace charge. Ashape which is particularly desirable from this aspect resembles apillow or loaf of bread and has slightly rounded edges.

Various processes for producing shaped coke are known in whichbriquettes or pellets made from coal or a coalcoke mixture are mixedwith hot, dine-grained heat carriers, such as sand or other fine-grainedmaterials. This mixing results in heating of the briquettes or pellets.In other known processes, shaped pieces of coal or coke are embedded insand and are carbonized by the action of hot gases to form a smokelessfuel. The shaped pieces to be carbonized are made from comminuted coalor from lowtemeprature coke or mixtures thereof. The coal and coke mayconsist of mixtures of components differing in origin. Fine-grained oreor mineral additives may be added to the carbonaceous material which isto be briquetted. The

3,700,564 Patented Oct. 24, 1972 ICC shaping is effected by apelletizing or briquetting operation with an addition of pitch, bitumen,bentonite, sulfite solution or other suitable known binders.

When it is desired to produce a shaped coke article which burns withoutforming smoke and soot and may be used as a fuel in heat-generatingfurnaces, it is suicient to carry out a heat treatment withoxygen-containing gases at low temperatures up to about 350 underoxidation conditions. The resulting briquettes have large residualcontents of volatile constituents .and Ia relatively low strength. Forthis reason they cannot be used for metallurgical purposes. When it isdesired to produce shaped metallurgical coke, particularly blast furnacecoke, a very high-temperature carbonization up to end temperaturesbetween 800 and 1000 C. has been found to be essential.

A known process for the high-temperature carbonization of fuelbriquettes with the aid of solid heat carriers utilizes a shaft furnace,in which highly heated sand and the shaped carbonaceous articles arejointly moved in `downwardly directed, concurrent streams. As thebriquettes enter the furnace, they are immediately subjected to thehighest treating temperatures. The rate of temperature rise at thesurface of the briquettes is initially very high and decreases as thetemperature equalization between the sand and the shaped carbonaceousarticles and between the surface and core of the shaped articlesproceed. This treatment is satisfactory only with a few fuels,particularly with low-gas fuels, and the shaped coke made therefrom hasin most cases only a moderate wear resistance. When shaped articles areused which have been made from coals containing more volatileconstituents, the shaped articles burst whereby producing small particlesized coke or a shaped coke which has much reduced mechanical strengthproperties as a result of internal stresses. For this reason, theabove-mentioned process of carbonizing shaped articles has been carriedout in two states with the shaped articles and the sand moved incountercurrent streams with respect to each case. The same disadvantageswill arise when pellets of coal or of mixed coal and ore are charged ina rotary kiln which is heated with combustion gases and where thepellets are embedded in a bed which is at a temperature of at leastabout 500 C. and in which the pellets are heated to an end temperatureof about 850 C. at a rate of about 30- 50 C. per minute.

U.S. Pat. 3,018,226 describes a process in which briquettes made from amixture of caking bituminous coal and non-caking coal or coke and ofpitch as a binder are carbonized by irst subjecting them to a heat shockso that the surfaces of the briquettes substantially immediately assumea temperature of between about 480 and 680 C., and the heating of thebriquettes is continued so that the surface of the briquettes remains inthat temperature range until the temperature has been equalizedthroughout the interior of the briquettes. The briquettes aresubsequently heated to temperatures in excess of 760 C. until thecontent of volatile constituents in the shaped coke article has beenreduced to below 2%. In this process, the briquettes may be heated withhot, inert gases or with fine-grained heat carriers and are preferablyheated in the rst stage in a fluid-ized bed.

U.S. Pat. 3,018,227 describes a process of producing shaped cokearticles in which briquettes made from a mixture of l0-35% by weight ofa moderately caking bituminous coal, -45% by weight of coke produced ina fluidized bed, and 6-20% by weight of pitch, are rapidly heated to atemperature which is higher than the plastic range of the briquettingmixture but lower than 677 C. and are carbonized until the temperaturehas been equalized throughout each briquette, whereafter the briquettesare subjected to dry distillation at a higher temperature.

We have found that such a heat shock treatment cannot be generallyapplied to briquettes made of all materials but will be withstood onlyby moderately caking briquette mixtures. When briquette mixturescontaining more highly caking coal are shocked (suddenly heated), theytend to form bubbles and foam in their interior to an increased degreeand often burst. Even if they do not burst, they are often so damaged byheat cracks that they break and splinter easily in further use. If thebriquette mixture is so lean that it will withstand the treatmentinvolved in that procedure, e.g. as a result of an addition ofnon-caking, low-gas coke or coke, the wear resistance and the crushingstrength of the resulting coke shaped article will be much reduced sothat it can no longer be used in a blast furnace.

It is an object of this invention to provide a novel method ofcarbonizing carbonaceous shaped articles which is less subject to thedisadvantages of prior art techniques.

It is another object of this invention to provide an improved cokearticle.

`Other and additional objects of this Iinvention will become apparentfrom a consideration of this entire specification including the drawingand claims hereof.

In accord with and fulfilling these objects, one aspect of thisinvention resides in the improved process of carbonizing pellets of thetype referred to above by subjecting such to an initial suddentemperature rise for such a time that only the outermost layer of eachpellet (briquette), which layer has a thickness of only a fewmillimeters, is rapidly heated above the plastic range of the coalmixture followed by subsequent resolidification. The carbonization ofthe inside of each briquette, however, must be carried out much 4slowerand should suitably begin at a temperature which is lower than thatwhich was used for the sudden heating of the surface layer. Thecompletion of carbonization of each briquette is carried out at a lowrate of temperature rise and the end temperature at which thetemperatures of the skin and core of each shaped article are equalizedis below 600 C. The briquettes which have thus been carbonized aresubsequently subjected to dry distillation at temperatures up to 1000 C.The highly different temperatures necessary in each of the severalstages of the treatment according to this invention are achieved throughthe use of fine-grained solid, particulate heat carriers.

The process according to the invention is characterized by treatingshaped carbonaceous articles in a first stage for two to `five minuteswith a solid, particulate heat carrier which is heated to SOO-600 C. andmoves concurrently with the shaped articles; treating the shapedarticles in a second stage for 30-90 minutes with a solid, particulateheat carrier which moves countercurrent or transverse current withrespect to the shaped articles and has an initial temperature of 40C-500C., increasing to SOO-600 C., and finally treating the shaped articlesin a third stage with a solid, particulate heat carrier which moves in acountercurrent or transverse current to the shaped articles and whichhas an initial temperature of S50-650 C., increasing to S50-1000 C.

The heat carrier consists preferably of sand. The ratio of the weight ofthe heat carrier to that of the shaped articles is about 2:1 to 4:1 inthe rst stage, about 3:1 to 6.1 in the second stage, and about 1:1 to2:1 in the third stage.

According to the invention, the shaped articles consisting of briquettesor pellets are supercially carbonized in the rst stage lby beingsuddenly heated with heat carriers at a temperature of about 50G-600 C.s0 that the surfaces of the shaped articles are suddenly heated abovethe plastic range of the briquette mixture and then suddenlyresolidiiied. The resolidilication should be restricted to a depth of 1to 3 millimeters. In the second stage, the temperature of the heatcarriers is reduced to about 450 C. The temperature of the heat carriersis then slowly increased at a rate of 0.5-2 C. per minute until atemperature between 500 and 600 C. has been reached so that this slowheating of the shaped articles for 30-90 minutes causes their core to beheated through the plastic temperature range of 40G-550 C. and to beresolidified. Temperatures above 600 C. will always be detrimentalduring the initial sudden heating and during the slow heating in thesecond stage. The reduction of the treating temperatures after theinitial sudden heating of the shaped articles is important to ensurethat there is sufficient time for the escape of the gases and vaporsreleased inside each briquette. Otherwise, the treatment would promotethe formation of large pores, bubbles or foam so that higher stresseswould be induced in the shaped articles.

When the shaped articles have been resolidiiied, they are subjected todry distillation in the third stage while being heated to a temperatureof 800-1000 C. at a rate of 3-10 C. per minute. It is desirable to heatthe shaped articles at a lower rate first and at a higher ratethereafter. During this treatment, the shaped articles move preferablycountercurrent or transverse current with respect to fine-grained solidheat carriers, which are at a temperatue of about S50-650 C. at thebeginning and at a temperature of about 850-1000 C. at the end of theiraction on the shaped articles.

The ratio of the weight of the heat carriers to that of the shapedarticles is about 2:1 to 4:1 in the first stage and should be sufficientto ensure that the soft, plastic briquettes are completely embedded inthe solid, particulate heat transfer medium. In the second stage, theratio of the weight of the heat carrier to that of the shaped articlesis in the range of about 3:1 to 6:1 so that a slow continuoustemperature rise is carried out in this stage. A temporary plastic stateof the shaped articles is accomplished in this range. In the thirdstage, in which a dry distillation is effected, a ratio of the weight ofthe heat carrier to that of the shaped articles of about 1:1 to 2:1 issufiicient.

The temperature profile during the countercurrent treatment with the hotheat carrier moving countercurrent thereto will depend on the ratio ofthe mass of the heat carrier to that of the shaped articles. If the massof the heat carrier is large so that the water equivalent is high, thetemperature rise will be initially rapid and slower thereafter. Thewater equivalent is the product of the mass and specific heat of theheat carrier.

Conversely, where the mass of the heat carrier is small, so that thewater equivalent is low, the temperature rise will be initially slow andfaster thereafter.

The times and temperatures for and at which the treatment is carried outmay be selected to influence the pore size and porosity of thecarbonized product so as to obtain desired values of these parameters. Atreatment for a longer time generally reduces the pore size and porositywhereas the use of a temperature at the upper limit so that the time ofthe treatment is reduced will result in larger pores and a higherporosity. The duration of the treatment and the upper temperature limitwill be selected in each case dependant on the caking and expansionproperties and the softening behavior of the coal-pitch mixture which isemployed. These are determined experimentally for the individual coalsand briquette mixtures used. It will be obvious that the carbonizationof shaped articles having a higher weight per article will take moretime than the carbonization of shaped articles having a lower weight perarticle.

The formation of proper pores is of great importance for the quality ofa metallurgical coke. The porosity is suitably between 40% and 50% andthe pores should not be too ne. Fine pores tend to become clogged moreeasily by soot or the like so that they become ineffective. Large poresdo not present a sufficiently large reaction area. Whereas thedisadvantage of the large pores is compensated to some extent by ahigher porosity, larger pores result in a lower bulk density and in mostcases in a lower Wear resistance. For this reason it is important toform medium size pores in the shaped article as far as possible. Theporosity and pore size may also be influenced by the caking capacity ofthe coal mixture and by the proportion of admixed binder, such as tarpitch or petroleum bitumen. If the porosity is too large, it may bereduced by using a leaner coal mixture and/or by a pre-admixing of thebinder. To increase the porosity, the carbonization time may be reducedor a coal mixture having a higher caking capacity may be used and/or theproportion of admixed binder may be increased. The caking capacity ofthe coal and the proportion of binder are suitably selected so that theshaped articles are subjected to temperatures in the range between aboutS50-600 C. for a time which is as short as possible, e.g., 30 minutes,so that the total time of the treatment is as short as possible and thecarbonizing apparatus has a high throughput capacity.

In the process according to the invention, shaped articles having ahigher caking and expansion capacity than those used before can becarbonized and processed into a high-grade shaped coke. As a result, theproportion of admixed non-caking coal or coke can be reduced, as isoften desired. On the other hand, the resulting shaped cake has internalstress cracks to a smaller extent and has a higher abrasion resistance.This is of great advantage particularly when the coke is to be used in ablast furnace.

Where coals having excessively high caking and expansion capacities areused in the process according to the invention it is desirable to use aleaner mixture because otherwise too long treatment times would berequired particularly in the second stage. This would increase thecapital and operating costs of the plant and reduce the overall economythereof. For this reason, such coals should be made lean but they neednot be so lean for being carbonized by the process according to theinvention as in the processes known before. To make the coal lean, anon-caking coal or a slightly caking coal or cokes of various kinds ororigins may be admixed to form the material to be briquetted. In manycases, suitable coal is not available and it is often undesirable andless economical to produce in a separate -plant additionalcoke for usein making a lean mixture. In such cases it may be desirable in `theproduction of blast furnace coke to add fine ore and/or lime to thebriquetting mixture before it is shaped. Fine ore and/or lime must beadded to the blast furnace in any case so that it may" be economical toincorporate such in the coke. When the shaped articles are carbonized,fine ore and/ or lime will reduce the caking and expansion capacity to alarger extent than non-caking coal'or coke. The heating in three stagesas taught by the invention is useful also with shaped articles whichhave moderate caking and expansion capacities and which could becarbonized by known processes. In these cases, the treatment can becarried out at temperatures at the upper limits of the ranges taught bythe invention and the duration of the treatment may be reduced so thatthe Iresulting shaped coke has a higher wear resistance and a lowertendency toV splinter than the shaped coke articles which can beproduced by the previously known processes.

The sudden heating of the shapedarticles in the first stage from abriquetting temperature of about 80 C. with pitch-bonded briquettes orfrom a similar temperature with dried pellets must not be carried outfor an excessively long time. By this treatment, only an outermost layerhaving a thickness of 1-3 millimeters should be rapidly heated above theplastic range and resolidited. If deeper layers are also subjected tothe rapid heating, larger pores and bubbles may be formed and/or theshaped articles may be splintered. For this reason, the sudden heatingshould be carried out for 2-5 minutes. A time at the lower limit will beused were the heat carrier is at a relatively high temperature and wherethe shape articles have a high tendency to cake and expand.

The fine-grained heat carrier consists preferably of sand having aparticle size of 0.2-2 millimeters, preferably of 0.5-1.0 millimeter.Other known particulate heating media which may be used includesillimanite, corundum, coke or the like.

The process according to the invention is preferably carried out in arotary kiln. During their suddent heating, the shaped articles aresuitably moved concurrently with the heat carrier, which is chargedtogether with the shaped articles to a rotary drum. For their slowsecond heating and mild treatment, the shaped pieces are desirably movedcountercurrent to the heat carrier, suitably in a rotary kiln havinginternal fixtures, such as disclosed in German patent application M75,578, P 15 83 472.7. The third heating stage for the dry distillationof the shaped articles can also be desirably performed in a rotary kilnin which the heat carrier is moved countercurrent to the shapedarticles.

Whereas all three heating stages may be combined in a single rotarykiln, it is particularly desirable for relatively large plants to carryout the third heating stage for dry distillation in a separate rotarykiln or even to provide separate rotary kilns for each of the threestages.

To perform the heating in three stages in accordance with the invention,the shaped articles may be advanced on a horizontal or inclined grateand the particulate heat carriers may ow downwardly through a layer ofsaid shaped articles in a transverse current. The temperatures and flowrates of the heat carriers may be selected so that the shaped articlescan be subjected to carbonization and dry distillation in accordancewith the invention in different portions of the overall length of thegrate. A bed which consists of sand, coke or the like and which iscontinuously or periodically iluidized may also be used in the firstheating stage.

The treatment in all three heating stages according to the invention orin one or two of said stages may be alternatively carried out with theaid of hot inert gases in a shaft furnace. This mode of operationrequires a higher expenditure, cannot be supervised as easily and doesnot result in a shaped coke having as uniform good quality. For thisreason, it is preferable to use fine-grained solid particulate heatcarriers in the carbonizing treatment according to the invention.

The process will now be explained more fully with refence to an exampleand the ligure, which is a schematic view of the process and apparatusof this invention.

In the figure, a first rotary kiln 1 is used to treat briquettes in thefirst stage and a second rotary kiln 2 to treat the briquettes in thesecond and third stages. Briquettes, at a temperature of about C., areintroduced at a rate of 1000 kilograms per hour into the first rotarykiln 1 through a conduit 3. Sand at a temperature of 550 C. isintroduced at the same time at a rate of 3000 kilograms per hour througha conduit 4 into the first rotary kiln 1. These briquettes and sand aremoved concurrently through the first rotary kiln, in which they residefor two minutes. During this treatment of the briquettes with aconcurrently moving heat carrier, the surface of the briquettes israpidly heated to a temperature which is similar to that of the sand.The briquettes are carbonized only at their surface whereas their coreportions are heated only slowly. In each briquette, a skin having athickness of 2-3 millimeters is hardened as a result of thecarbonization so that the briquettes are well able to withstand thesubsequent treatment.

The mixture of briquettes and sand is transferred by a chute 5 from thefirst rotary kiln 1 into the second rotary kiln 2. Immediately after themixture has been received by the rotary kiln 2, the mixture is separatedby screen fixtures 12. 'I'he briquettes are conveyed through the secondrotary kiln 2 to the other end thereof whereas the sand which has beenscreened off leaves the second rotary kiln 2 immediately through aconduit 7. Sand at 900 C. is charged through the conduit 6 at a rate of1250 kilolgrams per hour to the second rotary kiln 2 and is movedthroughout the length of the second rotary kiln countercurrent to thebriquettes. Sand at 500 C. is charged at a rate of 2500 kilograms perhour through a conduit 8 into the second rotary kiln and, by a centrallydisposed lance tube 9, is blown into the second rotary kiln 2approximately as far as to the middle thereof.

The briquettes charged to the second rotary kiln 2 are heated whilemoving countercurrent to the sand and in the first half of the rotarykiln are treated with a mixture of the sand from conduits 6 and 8. Thismixture has an initial temperature of 500 C. The sand is cooled to 400C. until it reaches that end of the rotary kiln where the briquettes arecharged and leaves the second rotary kiln 2 also, through conduit 7. Thebriquettes are slowly and continuously heated by the sand and in themiddle of the rotary kiln have a temperature of 520 C. at their surfaceand of 480 C. in their interior. While the coal is thus treated in aplastic state, it is subjected to a slow dry distillation during 40minutes without the occurrence of undesired` phenomena due to expansionor cracking.

In the second half of the rotary kiln, the briquettes are carbonizedwhile the carbonization of the briquettes is completed during anadditional period of 60 minutes while the briquettes are movedcountercurrent to the sand. During this time, the sand is cooled fromits inlet temperature of 900 C. to 550 C. and in the middle of therotary kiln is mixed with the sand which is charged through the lance.The resulting mixture is at a temperature of 500 C. 'Ihe drydistillation of the briquettes proceeds slowly and continuously. Coke ata temperature of 850 C. and at a rate of 700 kilograms per hour isdischarged from the second rotary kiln through a conduit 10 and issubsequently cooled. Part of the sand which is discharged at 7 is heatedto the temperature of 900 C. and is divided among conduits 3, 6 and 8,in which it is mixed with sand at a lower temperature. The vapors andgases which are thus evolved are vented through a conduit 11.

What is claimed is:

1. A process of producing shaped coke articles which comprises forming ashaped article comprising highly caking carbonizable carbonaceousmaterial; contacting said shaped articles with a solid, particulate heatcarrier for about 2 to 5 minutes in a iirst stage wherein said firststage heat carrier is at about 500 to 600 C. and moves concurrently withsaid shaped articles to raise to about 500 C. only up to about 3 mm. ofsaid shaped articles, contacting the shaped articles emerging from saidrst stage with a solid, countercurrently moving particulate heat carrierfor about 30 to 90 minutes in a second stage wherein said second stagehas an initial temperature of about 400 to 500 C. increasing to a finaltemperature of about 500 to 600 C., the temperature of said shapedarticles upon entering said second stage falling sufiiciently to hardenthe surfaces of said shaped articles; and contacting the shaped articlesemerging from said second stage with a solid, countercurrently movingparticulate heat carrier in a third stage wherein said third stage hasan initial temperature of about 550 C. to 650 C. increasing to about 850to 1000 C.

2. The process claimed in claim 1 wherein said heat carriers are sand.

3. The process claimed in claim 1 wherein the Weight ratio of heatcarrier to shaped article in said first stage is 2:1 to 4:1, in thesecond stage is 3:1 to 6:1 and in the third stage is 1:1 to 2: 1.

4. A shaped coke article produced by the process claimed in claim 1.

S. The process claimed in claim 1 wherein the contact with and heatingof said shaped articles by said heat carrier is elected in a rotarykiln.

References Cited UNITED STATES PATENTS 3,018,226 1/1962I Batchelor etal. 201-5 3,018,227 `l/l962 Baum et al. 201-23 3,444,046 5/ 1969 Harlow201-6 3,444,048 5/ 1969 Schmeling 201-12 FOREIGN PATENTS 503,199 5/1951Belgium 201--12 X NORMAN YUDKOFF, Primary Examiner D. EDWARDS, AssistantExaminer U.S. Cl. X.R. 201-l2, 20, 32, 44

